Choosing how to receive your Medicare coverage can feel like a big decision, and two of the most common paths — Medicare Advantage and Medigap — work in very different ways. One replaces the way Original Medicare delivers your benefits, while the other supplements Original Medicare and leaves that coverage in place. This guide walks through what each option is, how costs and coverage compare, when you are allowed to enroll, and which situations each plan type tends to suit. The goal is not to tell you which one to pick, but to give you plain-language facts you can bring to a conversation with a licensed benefits counselor.
Start With the Foundation: Original Medicare
Both paths build on Original Medicare, so it helps to understand what that baseline covers.
- Part A covers inpatient hospital stays, skilled nursing facility care after a qualifying hospital stay, hospice care, and some home health services.
- Part B covers doctor visits, outpatient care, preventive services, lab work, durable medical equipment, and many other medically necessary services.
The important detail: Original Medicare generally pays about 80% of approved Part B costs after the deductible, and it has no annual limit on your out-of-pocket spending. That 20% coinsurance, plus hospital deductibles, is the “gap” that both Medicare Advantage and Medigap are designed to address — in completely different ways.
What Is Medicare Advantage?
Medicare Advantage, also called Part C, is a private health plan that is approved by Medicare to deliver your Part A and Part B benefits. When you enroll in one, you typically stop using your red, white, and blue Medicare card for most services and use the plan’s card instead.
How it works
- Plans must cover everything Original Medicare covers, but they can set their own rules about how you receive that care.
- Most plans use a network of doctors, hospitals, and specialists. Common structures include health maintenance organizations, which generally require referrals and in-network care, and preferred provider organizations, which offer more flexibility at a higher cost.
- Prior authorization is often required before certain tests, procedures, or specialist visits.
- Most plans include prescription drug coverage as part of the package.
- Many plans add extras such as dental, vision, hearing aids, fitness memberships, or over-the-counter allowances.
What it costs
You still pay your standard Part B premium. On top of that, the plan sets its own copayments, coinsurance, and deductibles. Many plans advertise a low or even zero additional monthly premium, but that does not mean care is free — you pay each time you use services, and those costs can add up quickly during a hospital stay or a serious illness. Every Medicare Advantage plan does include an annual out-of-pocket maximum, which caps your in-network spending.
What Is Medigap?
Medigap, also called Medicare Supplement Insurance, is a private policy that pays some or all of the cost-sharing that Original Medicare leaves to you. You keep Original Medicare as your primary coverage and use your Medigap policy alongside it.
How it works
- In most states, Medigap policies are standardized. Plan letters such as A, B, D, G, K, L, M, and N must offer the same core benefits no matter which insurer sells them, which makes comparison much simpler.
- There are no provider networks. Any doctor, hospital, or specialist who accepts Medicare will generally accept your Medigap policy.
- No referrals and no prior authorization for Medicare-covered services.
- Coverage travels with you nationwide, and some plans include limited emergency care outside the country.
- Medigap does not include prescription drug coverage. You need a separate Part D drug plan.
What it costs
You pay your Part B premium plus a monthly Medigap premium, which is typically higher than what a Medicare Advantage plan charges. In return, your out-of-pocket costs when you actually use care are usually very low and predictable. Depending on the plan letter, Medigap may cover the Part A hospital deductible, the 20% Part B coinsurance, skilled nursing facility coinsurance, and some or all of the Part B deductible.
Side-by-Side Comparison
| Feature | Medicare Advantage (Part C) | Medigap (Medicare Supplement) |
|---|---|---|
| Relationship to Original Medicare | Replaces the delivery of Part A and Part B benefits | Sits alongside Original Medicare as secondary coverage |
| Provider choice | Usually a network; out-of-network care may not be covered | Any provider who accepts Medicare nationwide |
| Referrals and prior authorization | Often required | Not required for Medicare-covered care |
| Monthly premium | Often low; some plans have none beyond Part B | Higher, and varies by plan letter and age |
| Costs when you use care | Copays and coinsurance for many services | Generally minimal after premiums |
| Out-of-pocket limit | Yes, an annual cap for covered in-network care | Not needed — your exposure is already very low |
| Prescription drugs | Usually included | Not included; requires a separate Part D plan |
| Extra benefits | Often dental, vision, hearing, fitness, and more | None beyond Medicare-covered cost sharing |
| Enrollment flexibility | Can change plans during designated enrollment periods | Easiest to buy during your one-time open enrollment window |
Enrollment Rules and Timing
Timing matters enormously here, and it is one of the strongest arguments for planning ahead.
- Initial enrollment for Medicare runs for seven months around your 65th birthday: the three months before your birthday month, the month itself, and the three months after.
- Medigap open enrollment is a one-time, six-month window that begins the month you are 65 or older and enrolled in Part B. During this window, insurers cannot turn you down or charge you more because of your health history.
- After that window, in most states, insurers may use medical underwriting. That means a pre-existing condition could lead to a higher premium or a denial. Certain limited situations, such as losing other coverage, may give you a guaranteed right to buy a policy.
- Medicare Advantage can be joined during your initial enrollment period or during the annual enrollment period in the fall, with coverage typically starting January 1. There is also a January-through-March window to switch plans or leave a Medicare Advantage plan and return to Original Medicare.
- Trial right: if you try a Medicare Advantage plan and disenroll within the first year, you may have a guaranteed opportunity to buy certain Medigap policies in many states.
One practical warning: it is generally much easier to move from Medigap into Medicare Advantage than the reverse. If you drop a Medigap policy later, you may not be able to buy it back at the same terms.
Which Option Tends to Fit Which Situations?
These are general patterns, not recommendations for your personal situation.
- Medicare Advantage may appeal to people who want a lower monthly premium, are comfortable using a defined network, expect to need extra benefits such as dental or vision, and are willing to manage referrals and prior authorizations.
- Medigap may appeal to people who want predictable costs, travel frequently or split time between regions, see multiple specialists, or simply prefer not to deal with network restrictions and approvals.
- Budget matters in both directions. Medicare Advantage lowers fixed monthly costs but raises costs when you need care. Medigap raises fixed monthly costs but keeps care costs low and stable.
Questions Worth Asking Before You Decide
- Which doctors and hospitals do I want to keep, and are they in the network?
- What is the worst-case annual out-of-pocket cost if I have a serious health event?
- Does the plan cover my prescriptions, and are my specific drugs on the formulary?
- How much travel do I do, and would out-of-network care be covered?
- Am I still inside my one-time Medigap open enrollment window?
The Bottom Line
Medicare Advantage and Medigap solve the same problem in opposite ways. Medicare Advantage bundles hospital, medical, and usually drug coverage into a single network-based plan with lower premiums and higher point-of-care costs. Medigap leaves Original Medicare intact, adds predictable cost sharing, and gives you near-total freedom of provider choice in exchange for a higher monthly premium. The right fit depends on your health, your budget, your doctors, and your tolerance for paperwork and approvals — and the timing of your decision can matter as much as the choice itself.
Because plan details change every year, it is worth reviewing your options annually rather than assuming last year’s choice is still the best one. A licensed insurance counselor or your state’s health insurance assistance program can walk through your specific medications, providers, and budget at no cost. If you would like to keep building your understanding of coverage, costs, and preventive care, explore the related health and wellness topics on our site.